This invention relates to positive crankcase ventilation (PCV) systems for engines and, more particularly, to a PCV assembly and fitting for improving the assembly and operation of a PCV system.
It is known in the art to provide positive crankcase ventilation (PCV) systems for internal combustion engines to draw crankcase vapors from the engine crankcase into an intake air passage, such as in an intake manifold, and conduct the crankcase vapors with the air into the engine cylinders for burning and disposal through the engine exhaust emission control system. Ventilation of engine crankcases is desirable to remove water and fuel vapors as well as combustion byproducts which may accumulate in the crankcase during normal engine operation. Positive ventilation systems are desirable since they assure adequate crankcase ventilation while disposing of the crankcase vapors in the engine cylinders. There, substances such as hydrocarbons and combustion products are burned and treated with the engine exhaust gases prior to being released into the atmosphere.
A typical PCV system may include a PCV control valve or orifice mounted in a rocker cover or other suitable portion of the engine which communicates with the engine crankcase. The PCV valve or outlet fitting is connected by a tube or hose with a tubular connector or other suitable fitting communicating with the interior of the engine intake manifold, or another portion of the engine air intake system in which a vacuum is developed by throttling the intake. During engine operation, the vacuum developed in the manifold or other component draws crankcase vapors through the PCV system and fitting into the manifold where it is mixed with the intake air and delivered to the engine cylinders for burning with the fuel supplied by the engine fuel system.
When the engine is operated in very cold ambient temperatures, water that has accumulated in the engine oil and crankcase will vaporize and condense in the PCV system passages. The condensate may collect in the PCV passage where the delivery fitting enters the manifold due to loss of heat from the crankcase vapors to the fitting which is cooled by the walls of the manifold exposed to below freezing temperatures of the intake air. If the frost builds up in the passage it may become blocked, preventing the normal operation of the PCV system in disposing of crankcase vapors through the engine induction system and cylinders.
Various devices have been utilized to avoid frost build up and blocking of the PCV system. These include heating sensitive portions of the PCV passages with engine coolant in a heat transfer device, using electrical heaters to heat the PCV fitting or valve or to raise the temperature of the vapor in the PCV system, and utilizing a heat conductive strap wrapped around the PCV tube to conduct heat from the cylinder head to the tube. These solutions, while effective, add complexity to the design and installation of the engine PCV system as well as adding to its cost.
The present invention provides an improved PVC assembly and fitting which significantly reduces the possibility of vapors freezing so as to block the PCV passage. This is accomplished by using a plastic material, such as nylon, which has very low heat conductivity as compared to a metal fitting and which is also thermally isolated from the PCV inlet opening of the aluminum metal manifold to reduce heat loss from the fitting to the cold walls of the manifold.
A further feature of the invention is the use of a double seal arrangement on the fitting. A first O-ring seal in a groove of the fitting slides into a smooth portion of an inlet opening in the manifold PCV passage to seal against leakage around the body of the fitting. A second O-ring seal is mounted on a slightly larger diameter portion of the fitting and expands into a groove provided in the inlet opening of the manifold PCV passage as well as being held in a groove of the fitting. This second seal acts as an additional back-up seal as well as providing a snap in attachment for the fitting within the PCV inlet opening of the manifold. The seal also acts to retain the fitting within the inlet opening subject to removal by pulling on the fitting with a sufficient force. This feature provides quick connection of the PCV fitting to the manifold as well as allowing removal for service or replacement without requiring a separate fastener for attaching the fitting to the manifold.
An isolated portion of the fitting extends into the manifold air passage so that the crankcase vapors entering the air stream are not cooled excessively by adjacent portions of the manifold wall. Accordingly, freezing of the vapors within the PCV fitting is avoided and the PCV passage remains free for the flow of crankcase vapors.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.